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2004 GMC Yukon 5.3L Eng Base
INFORMATION ON GRADUAL COOLANT LOSS OVER TIME WITH NO
EVIDENCE OF LEAK FOUND
TECHNICAL SERVICE BULLETIN
Reference Number(s): 06-06-01-019B, Date of Issue: June 12, 2007
2004-2006 Buick Rainier; 2001-2006 Cadillac Escalade Models; 2001-2006
Chevrolet Avalanche, Blazer, Silverado, Suburban, Tahoe, TrailBlazer Models;
Affected
2001-2006 GMC Envoy, Jimmy, Sierra, Yukon Models; 2001-2004 Oldsmobile
Model(s):
Bravada; 2005-2006 Saab 9-7X; with 4.8L or 5.3L VORTEC(R) GEN III, GEN IV V8
Engine (VINs V, T, M, B, Z - RPOs LR4, LM7, LH6, L33, L59)
This bulletin is being revised to include engine RPO L59. Please discard Corporate
Supercedes:
Bulletin Number 06-06-01-019A (Section 06 - Engine/Propulsion System).
SERVICE INFORMATION
Some vehicles may experience a gradual coolant loss over time. A very low percentage of
cylinder head(s) manufactured with an embossed Castech logo may develop a porosity crack in
a very specific area.
Inspect the cylinder head assembly to determine if the casting was manufactured by Castech.
This can be accomplished by inspecting for their casting logo located on top of the intake port,
under the rocker arm support rail and in the spring deck cavity portion of the cylinder head.
IMPORTANT: If the cylinder head(s) are Not a Castech casting, follow normal
diagnostic procedures in SI to determine the cause of the coolant loss.
Refer to the following illustrations on how to identify Castech casting and/or the very specific
areas of the cylinder head(s) for a coolant leak from porosity.
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Fig 1: Locating Logo
Courtesy of GENERAL MOTORS CORP.
Cylinder head(s) location of the Castech manufacturing casting logo (1).
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Fig 2: Close Up View Of Cylinder Head
Courtesy of GENERAL MOTORS CORP.
Close up view of the cylinder head(s) showing the Castech manufacturing casting logo (1).
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Fig 3: Inspecting For Witness Marks
Courtesy of GENERAL MOTORS CORP.
If the cylinder head(s) is a Castech casting (1), inspect the area around the five oil drain holes
for witness marks indicating coolant seepage over time (2).
IMPORTANT: If No evidence of coolant loss is found on inspection of Castech
casting cylinder head(s), follow normal diagnostic procedures in SI to determine the
cause of the coolant loss.
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Fig 4: Crack Location
Courtesy of GENERAL MOTORS CORP.
The crack location can be found in any of the five cylinder head(s) oil drains. This can be seen
as a clean or shiny area, on an otherwise stained surface (1). Pressurizing the cooling system at
this time may reveal coolant, air, or a combination, weeping in the described area. If inspection
reveals evidence of coolant witness marks (1), replace the entire cylinder head(s) assembly.
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